Resin additives such as phenolic antioxidants, ultraviolet absorbers and hindered amine compounds are generally known to inhibit deterioration of organic matters such as synthetic resins caused by light and heat.
Generally, a compound to be used as a resin additive is preferably one which has a high melting point and shows limited resin plasticization and evaporation from a resin, such as tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxymethyl)methane or tris(2,4-di-tert-butylphenyl)phosphite. However, an additive having an excessively high molecular weight cannot move in a resin, so that its stabilizing effect tends to be small.
Meanwhile, low-melting-point compounds such as stearyl(3,5-di-tert-butyl-4-hydroxyphenyl)propionate and bis(2,2,6,6-tetramethylpiperidyl)sebacate have relatively low molecular weight and thus exhibit excellent initial stabilizing effect; however, since they readily evaporate from a resin, their long-term stabilizing effect is poor. In addition, those compounds that are in a liquid, viscous or powder form adhere with each other to generate large aggregates or the like during storage and are thus poor in terms of the ease of handling; therefore, in order to improve the ease of handling, these compounds are required to be masterbatched.
However, when an ordinary resin additive such as a hindered amine compound or a benzoate compound is incorporated into a polyolefin resin, because of the low compatibility of the additive with the resin, in the preparation of a masterbatch comprising such a resin additive at a high concentration, there occurs a condition where the hindered amine compound or benzoate compound bleeds out to the pellet surface and the resulting pellets adhere to each other to form aggregates is generated, that is, a problem of clumping. Particularly, in the case of a hindered amine compound having a low melting point (for example, a melting point of not higher than 65° C.), since it melts and bleeds out under high temperature of summertime or the like, there is a problem in terms of the storage stability (clumping resistance). Therefore, only about 50 parts by mass of such a hindered amine compound can be incorporated with respect to 100 parts by mass of polyolefin, presenting not much advantage in masterbatching.
Particularly, those hindered amine compounds obtained by reaction between 2,2,6,6-tetramethyl piperidinol and fatty acid exhibit excellent weather resistance-imparting effect; however, they are likely to be in a liquid form at a low molecular weight. Thus, when such a hindered amine compound is masterbatched with a resin for the purpose of improving the ease of handling, there is a problem that the additive is likely to bleed out to the surface of the resulting masterbatched resin composition to show adhesive property.
On the other hand, inorganic fillers such as talc do not have such problems of clumping and the like and can thus be incorporated at a high concentration. For example, Patent Document 1 discloses a masterbatch composition comprising talc at a high concentration of 80 to 40 parts by mass with respect to 20 to 60 parts by mass of a resin.
Further, as a method for improving the surface tackiness caused by bleeding of an additive component in a resin additive masterbatch, for example, Patent Document 2 proposes a method in which tackiness is suppressed by masterbatching with the use of an organic metal salt.